1. Field of the Invention
This invention relates to a micrometer, and a method for manufacturing cylindrical component for a micrometer. More specifically, it relates to a micrometer of which manufacturing cost and weight is reduced and a method for manufacturing an outer sleeve and a thimble used as components of the micrometer.
2. Description of the Related Art
As shown in FIG. 19, a micrometer comprises an almost U-shaped main body 101, an anvil 102 held at an end portion of the main body 101, a spindle 104 screwed into the other end portion of the main body 101 through an inner sleeve 103 to-move toward and away from the anvil 102, an outer sleeve 105 placed and fixed onto the outside of the inner sleeve 103, a thimble 106 rotatably covered on the outside of the outer sleeve 105 and integrally connected with the spindle 104, and a ratchet mechanism 107 which slips when an excess load is applied on the spindle 104, and is provided at the rear end of the spindle 104.
On the outer circumferential surface of the outer sleeve 105, graduations 108A and numerals 108B of a main scale are formed at a predetermined pitch along the axial direction, and on the outer circumferential surface of the thimble 106, a graduation 109 of a vernier scale is formed at a predetermined pitch along the circumferential direction. By these graduations 108, 109, the amount of displacement of the spindle 104 to the anvil 102 can be measured. In other words, dimensions of the object which is held between the anvil 102 and the spindle 104 can be measured.
Conventionally, in forming the graduations 108A, 109A and numerals 108B, 109B, after the outlines of the graduations 108A, 109A and numerals 108B, 109B are formed by means of engraving or carving on the outer circumferential faces of the outer sleeve 105 and the thimble 106 fabricated in a predetermined cylinderical shape in advance, sumi ink is coated in the formed outlines, and then a baking treatment is carried out.
In the conventional forming method of the graduations 108A, 109A and numerals 108B, 109B, however, since the outlines of the graduations 108A, 109A and numerals 108B, 109B need to be carved or engraved one by one, considerable effort and time are required. Furthermore, after sumi ink is coated on portions formed by engraving or carving, the baking treatment is performed, so that the number of processes and costs are increased.
Since the outer sleeve 105 and the thimble 106 are conventionally formed of metal, they are heavy in weight and also bring up a disadvantage of spoiling the handling properties and operability, for a micrometer which to measure an object while holding it in one hand.
It is an object of the present invention to provide a micrometer which enables reduction in cost and weight.
It is another object of the present invention to provide manufacturing method of a cylindrical component for micrometer such as an anvil and a thimble which makes it possible to reduce the cost and the size.
A micrometer according to present invention, which comprises a main body holding an anvil at one end portion thereof and a spindle moving to and away from the anvil at the other end portion thereof through an inner sleeve, an outer sleeve covering the outside of the inner sleeve and fixed thereon, and a thimble unitedly connected to the spindle on the outside of the outer sleeve in a manner that the thimble rotates, said outer sleeve being provided with graduations and numerals on the outer circumferential surface along the axial direction, and the thimble being provided with graduations and numerals on the outer circumference thereof, is characterized in that at least one of said outer sleeve and said thimble comprises a base tube formed of a first resin and having the graduations protruding toward the outside on the outer circumferential surface thereof at predetermined intervals, and an outer skin formed of a second resin having a different color from that of the first resin and covering the outer circumference of said base tube except for the graduations, and the numerals are formed adjacent to the graduations.
According to the micrometer as structured above, since at least one of the outer sleeve and the thimble is formed with the graduations through the double-color molding using two kinds of resin having different colors, the cost and time needed for the manufacturing is reduced as compared with a conventional method for forming graduations by means of carving or engraving.
Furthermore, since the micrometer is made of resin, the weight is reduced as compared with a micrometer made of metal to improve the handling properties and operability of a micrometer in the measurement while being held with a hand.
In the aforementioned structure, for example, the second resin may be a resin which changes color thereof by irradiation of a laser beam, and the numerals may be formed by a discolored layer discolored by irradiation of the laser beam.
Alternatively, the second resin may be a resin peelable by irradiating a laser beam, and the numerals may be formed by a slit made by peeling of the second resin by the irradiation of the laser beam.
Thus, the numerals are formed efficiently.
The numerals as well as the graduations may be formed by the first resin to protrude outwardly on the base tube, and the outside of the base tube except for the graduations and the numerals may be covered with the outer skin.
By the above structure, the micrometer is formed including the graduations and the numerals through the double-color molding using two kinds of resin having different colors, in other words, the micrometer is formed with the numerals by means of the double-color molding, so that the manufacturing cost and the time for manufacturing are reduced further than the micrometer having the aforementioned structure.
Any structure can be employed for the main body. For example, it is advisable that the main body has a frame formed by a bending process of a metal plate formed in a predetermined shape, and the frame is formed with an anvil holding portion for holding the anvil on an end thereof and an inner sleeve holding portion for holding the inner sleeve on the other end thereof by a bending process.
In this point, as the metal plate, materials being light in weight and having high rigidity is preferable, such as a cold-rolled steel (SPC-C). Compared with a casting obtained by a conventional casting, the cost and the weight are reduced while the deformation caused by a measuring force is restrained, that is, the rigidity required in measuring is retained since the frame formed by means of bending the metal plate is used. As a result, the weight of the main body as well as the outer sleeve and the thimble is reduced, so that the total weight of the micrometer is reduced. Therefore, the improvement of the handling properties and the operability is promised. Moreover, since the weight of the micrometer is reduced not partially but totally, the weight balance which is an important property in using a micrometer can be maintained good.
A method for manufacturing a cylindrical component for a micrometer according to the present invention, the cylindrical component for a micrometer having graduations and numerals on the outer circumferential surface of a base tube thereof along the axial direction, is characterized by comprising the steps of molding primary molding product by a first resin, the primary molding product having the base tube and the graduations protruding outwardly on the outer circumferential surface of the base tube along the axial direction at predetermined intervals, forming outer skin by a second resin to cover the outside of the base tube except for the graduations, the second resin having a different color from that of the first resin, and irradiating a laser beam on the outer skin to form the numerals thereon.
According to the aforementioned methods, the base tube and the primary molding product having the graduations protruding outwardly from the outer circumferential surface of the base tube are formed first using the first resin, and using the second resin with a different color from that of the first resin, the outer skin is formed to cover the outside of the base tube except for the graduations, and then the numerals are formed on the outer skin by means of irradiating a laser beam. Therefore, the manufacturing cost and the time for manufacturing are decreased further than that of the conventional method manufacturing an outer sleeve and a thimble for a micrometer. Moreover, since the micrometer is made of resin, the weight is reduced as compared with the formation with metal.
In the aforementioned structure, in order to form the numerals on the outer skin, for example, the second resin may be a resin which changes color thereof by irradiation of a laser beam, and a laser beam is irradiated on the second resin to change color thereof on the irradiated portion to form the numerals by the discolored layer.
Alternatively, the second resin may be a resin peelable by irradiating a laser beam, and a laser beam is irradiated on the second resin to peel off the irradiated portion of the second resin and to form the numerals by slits thereby formed.